The invention relates to a transport container for maintaining the temperature of frozen goods, in particular frozen biological tissue samples or cell cultures.
Clinical diagnostics and research often require quick analysis of tissue samples in external specialist laboratories in order to obtain results for a decision regarding therapy. The analysis methods used (e.g. RNA analyses, protein markers) are rapidly developing. Deep freezing a sample has proven to destroy the least amount of information contained therein. Since research leads to the discovery of new markers on an almost daily basis, conserving the information is important, and it makes sense not only to subject the sample to the currently available examinations but also to conserve the samples as permanently as possible by deep freezing. Should the patient develop a problem in the months or even years after the sample was taken, e.g. suffer a relapse and require therapy, renewed examination of the original sample using analysis methods which may still have been unknown when the sample was taken could be of assistance and could indicate a promising targeted, expensive modern therapy in place of an untargeted standard therapy, and justify this financially to the benefactors.
Hence, it is important to have a transport container for sending frozen individual samples and which reliably avoids a transport-dependent break of the closed freezing chain while having a design which is as small and light as possible, which satisfies existing regulations, and keeps the sending costs low. Although the complexity and costs of sending can be reduced to a certain extent by collecting samples and sending them together, with a collection period of at most five days being feasible, this does however lead to administrative and logistical complexities, with intermediate storage of the samples at very low temperatures becoming necessary. Only a very small number of hospitals have a chest freezer required for this purpose, which can cool down to −70° C. for example.
WO 2005/066 559 A2 has already disclosed a transport container for maintaining the temperature of frozen biological tissue samples and cell cultures. It comprises an insulation container which is accessible via an insulating cover part and has superinsulation with a thermal conductivity λ≦0.002 W/(mK). A cooling container comprising a coolant chamber is provided in the insulation container, which coolant chamber surrounds a sample chamber for the frozen goods except for an access opening on the fastener side; the coolant chamber is permanently hermetically sealed, and comprises a coolant which emits the cold by solid/liquid phase transition. The coolant undergoes phase transition in the temperature range between −15° and −100° C., in particular between −30° and −85° C. and has a heat of fusion of at least 50 J/ml.
The cooling container with the coolant chamber and the sample chamber can be removed from the insulation container in this known transport container. The sample chamber extends almost to the upper end of the cooling container. The metallic inner wall of the insulation container merges into the outer wall and there is metallic contact between them.
This known embodiment already affords the possibility of maintaining the temperature of frozen samples for a number of days by using a coolant with a high heat of fusion and by means of the superinsulation with low thermal conductivity; however, the prescribed stringent requirements cannot always be reliably fulfilled because thermal bridges are present, as a result of which the coolant can be exhausted prematurely due to the detrimental influx of heat, and hence this can lead to a loss of information in the sample. Moreover, it was found that the handling of the known transport container is not yet ideal.